From 330b41295c258a7fc928e9ff85e83df60ba59973 Mon Sep 17 00:00:00 2001
From: Compot Developer <compot@openipc.org>
Date: Mon, 19 Oct 2026 21:29:07 +0000
Subject: [PATCH 1/6] feat: per-slot Mirror in the camera settings (#226)

Mirror flips the picture left to right, after the slot's Turn, in the
single view and the grid. A SurfaceView cannot be mirrored with
setScaleX(-1) and KEY_ROTATION has no mirror, so a mirrored H.264/H.265
slot renders through GlMirror: the decoder outputs into a SurfaceTexture
and an OpenGL ES 2 renderer on its own thread draws each frame turned
and flipped onto the view's surface. Unmirrored slots keep the decoder
drawing straight onto the SurfaceView (#76). The GL path is released
after the decoder, so the view's surface is free for the next one; if
EGL fails, the picture is shown unmirrored. MJPEG is flipped while it
is drawn in software (the hardware JPEG decoder cannot mirror).

The single view's layout now asks the decoder whether it swaps the
picture's sides, which covers the GL path's turn on any Android version.
/stats.json gets mirror: true for mirrored slots and cells.
---
 README.md                                     |   2 +-
 README.ru.md                                  |   2 +-
 README.zh-CN.md                               |   2 +-
 .../java/com/openipc/decoder/Decoder.java     |  22 +-
 .../java/com/openipc/decoder/GlMirror.java    | 319 ++++++++++++++++++
 .../com/openipc/decoder/JpegRenderer.java     |  12 +-
 .../openipc/decoder/MediaCodecManager.java    |  67 +++-
 .../java/com/openipc/decoder/MenuManager.java |   9 +-
 .../java/com/openipc/decoder/QuadCell.java    |   6 +-
 .../java/com/openipc/decoder/RtspClient.java  |   3 +
 .../java/com/openipc/decoder/RtspSession.java |   6 +
 .../com/openipc/decoder/GlMirrorTest.java     |  47 +++
 docs/debug.md                                 |   2 +-
 docs/usage.md                                 |   5 +-
 14 files changed, 478 insertions(+), 26 deletions(-)
 create mode 100644 android/app/src/main/java/com/openipc/decoder/GlMirror.java
 create mode 100644 android/app/src/test/java/com/openipc/decoder/GlMirrorTest.java

diff --git a/README.md b/README.md
index 9e693dd..7551eeb 100644
--- a/README.md
+++ b/README.md
@@ -65,7 +65,7 @@ A beta channel is available on [Google Play](https://play.google.com/apps/intern
    ```
    rtsp://username:password@ip_address:554/stream=0
    ```
-   Under the URL you can choose the transport; Auto (UDP, falling back to TCP) is the default for a new slot. Below it, **Turn** turns the picture of a camera mounted sideways or upside down. Other URL types: [Transports](docs/transports.md).
+   Under the URL you can choose the transport; Auto (UDP, falling back to TCP) is the default for a new slot. Below it, **Turn** turns the picture of a camera mounted sideways or upside down, and **Mirror** flips it left to right. Other URL types: [Transports](docs/transports.md).
 4. Press **Save**. The app connects straight away and reconnects automatically if the stream drops.
 
 ## Controls
diff --git a/README.ru.md b/README.ru.md
index d1b7d8a..7741cf2 100644
--- a/README.ru.md
+++ b/README.ru.md
@@ -65,7 +65,7 @@
    ```
    rtsp://username:password@ip_address:554/stream=0
    ```
-   Под адресом можно выбрать транспорт; у нового слота по умолчанию Auto (UDP с откатом на TCP). Ниже настройка **Turn** поворачивает картинку камеры, установленной боком или вверх ногами. Другие виды адресов — в [Transports](docs/transports.md) (на английском).
+   Под адресом можно выбрать транспорт; у нового слота по умолчанию Auto (UDP с откатом на TCP). Ниже настройка **Turn** поворачивает картинку камеры, установленной боком или вверх ногами, а **Mirror** отражает её слева направо. Другие виды адресов — в [Transports](docs/transports.md) (на английском).
 4. Нажмите **Save**. Приложение сразу подключится и само переподключится, если поток прервётся.
 
 ## Управление
diff --git a/README.zh-CN.md b/README.zh-CN.md
index cab2fcf..f23354a 100644
--- a/README.zh-CN.md
+++ b/README.zh-CN.md
@@ -65,7 +65,7 @@
    ```
    rtsp://username:password@ip_address:554/stream=0
    ```
-   地址下方可选择传输方式，新槽位默认为 Auto（优先 UDP，必要时回退到 TCP）。其下的 **Turn** 可旋转画面，适用于侧装或倒装的摄像机。其他地址格式见 [Transports](docs/transports.md)（英文）。
+   地址下方可选择传输方式，新槽位默认为 Auto（优先 UDP，必要时回退到 TCP）。其下的 **Turn** 可旋转画面，适用于侧装或倒装的摄像机；**Mirror** 可将画面左右镜像。其他地址格式见 [Transports](docs/transports.md)（英文）。
 4. 点击 **Save**。应用会立即连接；视频流中断时会自动重连。
 
 ## 操作说明
diff --git a/android/app/src/main/java/com/openipc/decoder/Decoder.java b/android/app/src/main/java/com/openipc/decoder/Decoder.java
index 33896c1..8d11f02 100755
--- a/android/app/src/main/java/com/openipc/decoder/Decoder.java
+++ b/android/app/src/main/java/com/openipc/decoder/Decoder.java
@@ -140,6 +140,8 @@ public class Decoder extends Activity
     private final Transport.Mode[] mTransports = new Transport.Mode[CAM_COUNT];
     /** Per slot (#201): degrees counter-clockwise, -1 for Auto (from the URL). */
     private final int[] mRotates = new int[CAM_COUNT];
+    /** Per slot (#226): the picture flipped left↔right. */
+    private final boolean[] mMirrors = new boolean[CAM_COUNT];
     private int mActive;
     private volatile String mHost;
     private String mVersion;
@@ -212,12 +214,9 @@ protected void onCreate(Bundle savedInstanceState) {
         // --- Create managers ---
         videoDecoder = new MediaCodecManager(new MediaCodecManager.Listener() {
             @Override public void onResolutionChanged(int w, int h) {
-                // The decoder turns the picture (#201, Android 6+ as in MediaCodecManager): a
-                // quarter turn swaps its sides
-                RtspClient c = rtspClient;
-                int r = c != null && Build.VERSION.SDK_INT >= Build.VERSION_CODES.M
-                        ? c.rotate() : 0;
-                if (r == 90 || r == 270) updateResolution(h, w);
+                // A quarter turn by the decoder (#201, Android 6+) or by the mirror's GL path
+                // (#226, any version) swaps the picture's sides
+                if (videoDecoder.swapsSides()) updateResolution(h, w);
                 else updateResolution(w, h);
             }
             @Override public void onDecoderStarted() { removeClearOverlay(); }
@@ -591,7 +590,7 @@ private void restartClean() {
 
     @Override
     public void onShowSettings() {
-        menuManager.showUrlEditor(mActive, mHosts, mTransports, mRotates);
+        menuManager.showUrlEditor(mActive, mHosts, mTransports, mRotates, mMirrors);
     }
 
     @Override
@@ -606,12 +605,14 @@ public void onShowSettings() {
     private void configureClient() {
         rtspClient.configure(mHost, mUserAgent, mTransports[mActive]);
         rtspClient.setSlotTurn(mRotates[mActive]);
+        rtspClient.setSlotMirror(mMirrors[mActive]);
     }
 
     private void createDecoder() {
         videoDecoder.setSurface(mVideoSurface);
         RtspClient c = rtspClient;
         videoDecoder.setRotation(c != null ? c.rotate() : 0);
+        videoDecoder.setMirror(c != null && c.mirror());
         videoDecoder.createDecoder(codecH265);
     }
 
@@ -652,6 +653,7 @@ private void loadSettings() {
             // Auto for a slot that has never stored one (#112)
             mTransports[i] = Transport.Mode.stored(pref.getString("transport_" + i, null));
             mRotates[i] = pref.getInt("rotate_" + i, -1);
+            mMirrors[i] = pref.getBoolean("mirror_" + i, false);
             // Plain URLs from older versions are re-saved encrypted right away
             if (credentials.needsMigration(stored)) {
                 if (migrate == null) migrate = pref.edit();
@@ -715,6 +717,7 @@ private void saveSettings() {
                     credentials.sealForSlot(mHosts[i], mUnreadable[i], DEFAULT_URL));
             edit.putString("transport_" + i, mTransports[i].name());
             edit.putInt("rotate_" + i, mRotates[i]);
+            edit.putBoolean("mirror_" + i, mMirrors[i]);
         }
         edit.apply();
 
@@ -1025,6 +1028,7 @@ private void createQuadCells() {
             quadCells[i] = new QuadCell(i, url, mode, quadViews[i], framePool, mUserAgent,
                     index -> runOnUiThread(() -> removeQuadOverlay(index)));
             quadCells[i].setSlotTurn(i < CAM_COUNT ? mRotates[i] : -1);
+            quadCells[i].setSlotMirror(i < CAM_COUNT && mMirrors[i]);
             quadCells[i].start();
         }
         quadAudio = getSharedPreferences("settings", MODE_PRIVATE).getInt("quad_audio", -1);
@@ -1629,6 +1633,7 @@ private Map<String, Object> debugState() {
             // Turned counter-clockwise, "size" is the turned one (#200, #201)
             int rotate = rtspClient != null ? rtspClient.rotate() : 0;
             if (rotate != 0) single.put("rotate", rotate);
+            if (rtspClient != null && rtspClient.mirror()) single.put("mirror", true);
             m.put("single", single);
         }
         QuadCell[] cells = quadCells;
@@ -1674,6 +1679,7 @@ private Map<String, Object> debugState() {
                     Map<String, Object> hb = cell.heartbeatStats();
                     if (hb != null) c.put("heartbeat", hb);
                     if (cell.rotate() != 0) c.put("rotate", cell.rotate());
+                    if (cell.mirror()) c.put("mirror", true);
                 }
                 list.add(c);
             }
@@ -2291,7 +2297,7 @@ private boolean drawJpeg(Frame frame, int gen) {
         Surface s = mVideoSurface;
         RtspClient client = rtspClient;
         int rotate = client != null ? client.rotate() : 0;
-        int[] size = jpegRenderer.render(frame, s, rotate,
+        int[] size = jpegRenderer.render(frame, s, rotate, client != null && client.mirror(),
                 () -> gen == listenerGen && s == mVideoSurface);
         if (size != null) jpegShown(size[0], size[1]);
         return size != null;
diff --git a/android/app/src/main/java/com/openipc/decoder/GlMirror.java b/android/app/src/main/java/com/openipc/decoder/GlMirror.java
new file mode 100644
index 0000000..e76c0c2
--- /dev/null
+++ b/android/app/src/main/java/com/openipc/decoder/GlMirror.java
@@ -0,0 +1,319 @@
+/*
+ * Copyright (c) OpenIPC  https://openipc.org  Prosperity Public License 3.0.0
+ *
+ * GlMirror.java — draws a decoder's output mirrored (and turned) onto a surface with OpenGL ES
+ *
+ */
+
+package com.openipc.decoder;
+
+import android.graphics.SurfaceTexture;
+import android.opengl.EGL14;
+import android.opengl.EGLConfig;
+import android.opengl.EGLContext;
+import android.opengl.EGLDisplay;
+import android.opengl.EGLSurface;
+import android.opengl.GLES11Ext;
+import android.opengl.GLES20;
+import android.os.Handler;
+import android.os.HandlerThread;
+import android.util.Log;
+import android.view.Surface;
+
+import java.nio.ByteBuffer;
+import java.nio.ByteOrder;
+import java.nio.FloatBuffer;
+import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.TimeUnit;
+
+/**
+ * A slot with Mirror on (#226): the decoder renders into a SurfaceTexture, and every frame is
+ * drawn onto the view's surface flipped left↔right and turned like the slot's Turn. A
+ * SurfaceView cannot be mirrored with setScaleX(-1) (the system composes it), and
+ * MediaFormat.KEY_ROTATION has no mirror, so this path is used only for mirrored slots; the
+ * others keep the decoder drawing straight onto the SurfaceView (#76).
+ *
+ * Everything GL runs on one thread of its own. Release the decoder before this, so its output
+ * surface is gone when the EGL surface leaves the view's surface.
+ */
+final class GlMirror implements SurfaceTexture.OnFrameAvailableListener {
+    private static final String TAG = "OpenIPCDecoder";
+    private static final long SYNC_TIMEOUT_MS = 2_000;
+
+    private static final String VERTEX =
+            "uniform mat4 uMvp;\n"
+            + "uniform mat4 uSt;\n"
+            + "attribute vec4 aPos;\n"
+            + "attribute vec4 aTex;\n"
+            + "varying vec2 vTex;\n"
+            + "void main() {\n"
+            + "  gl_Position = uMvp * aPos;\n"
+            + "  vTex = (uSt * aTex).xy;\n"
+            + "}\n";
+    private static final String FRAGMENT =
+            "#extension GL_OES_EGL_image_external : require\n"
+            + "precision mediump float;\n"
+            + "varying vec2 vTex;\n"
+            + "uniform samplerExternalOES sTex;\n"
+            + "void main() {\n"
+            + "  gl_FragColor = texture2D(sTex, vTex);\n"
+            + "}\n";
+    /** Triangle strip over the whole surface: x, y, then u, v. */
+    private static final float[] QUAD = {
+            -1f, -1f, 0f, 0f,
+            1f, -1f, 1f, 0f,
+            -1f, 1f, 0f, 1f,
+            1f, 1f, 1f, 1f,
+    };
+
+    private final HandlerThread thread;
+    private final Handler handler;
+    private final float[] mvp;
+    private final float[] st = new float[16];
+    private final FloatBuffer quad;
+
+    private EGLDisplay display = EGL14.EGL_NO_DISPLAY;
+    private EGLContext context = EGL14.EGL_NO_CONTEXT;
+    private EGLSurface window = EGL14.EGL_NO_SURFACE;
+    private int program;
+    private int texture;
+    private int uMvp, uSt, aPos, aTex;
+    private SurfaceTexture surfaceTexture;
+    private Surface input;
+    private boolean released;
+    private volatile int framesDrawn;
+
+    private GlMirror(int turnCcw, boolean mirror) {
+        mvp = transform(turnCcw, mirror);
+        quad = ByteBuffer.allocateDirect(QUAD.length * 4).order(ByteOrder.nativeOrder())
+                .asFloatBuffer();
+        quad.put(QUAD).position(0);
+        thread = new HandlerThread("gl-mirror");
+        thread.start();
+        handler = new Handler(thread.getLooper());
+    }
+
+    /**
+     * The position transform: turned {@code turnCcw} degrees counter-clockwise, then flipped
+     * left↔right on the screen when {@code mirror}, so Mirror always swaps the sides of the
+     * picture as it is shown, whatever the turn.
+     */
+    static float[] transform(int turnCcw, boolean mirror) {
+        // Quarter turns are exact; column-major, as glUniformMatrix4fv takes it
+        int t = ((turnCcw % 360) + 360) % 360;
+        float c = t == 0 ? 1f : t == 180 ? -1f : 0f;
+        float s = t == 90 ? 1f : t == 270 ? -1f : 0f;
+        float f = mirror ? -1f : 1f;
+        return new float[] {
+                f * c, s, 0f, 0f,
+                -f * s, c, 0f, 0f,
+                0f, 0f, 1f, 0f,
+                0f, 0f, 0f, 1f,
+        };
+    }
+
+    /** Where the point (x, y) of the full-surface quad lands with {@code m} (for tests). */
+    static float[] map(float[] m, float x, float y) {
+        return new float[] {m[0] * x + m[4] * y + m[12], m[1] * x + m[5] * y + m[13]};
+    }
+
+    /** Set up on {@code target}; throws when EGL or GL cannot. Decode into {@link #input()}. */
+    static GlMirror create(Surface target, int turnCcw, boolean mirror) throws Exception {
+        GlMirror g = new GlMirror(turnCcw, mirror);
+        try {
+            g.runSync(() -> g.setUp(target));
+        } catch (Exception e) {
+            g.release();
+            throw e;
+        }
+        return g;
+    }
+
+    /** The surface the decoder renders into. */
+    Surface input() { return input; }
+
+    /** Frames drawn onto the view's surface so far. */
+    int framesDrawn() { return framesDrawn; }
+
+    /** Release GL and the thread; waits until the view's surface is free again. */
+    void release() {
+        try {
+            runSync(this::tearDown);
+        } catch (Exception e) {
+            Log.w(TAG, "Mirror release: " + e.getMessage());
+        }
+        thread.quitSafely();
+    }
+
+    private interface Task {
+        void run() throws Exception;
+    }
+
+    private void runSync(Task task) throws Exception {
+        final Exception[] failure = new Exception[1];
+        CountDownLatch done = new CountDownLatch(1);
+        if (!handler.post(() -> {
+            try {
+                task.run();
+            } catch (Exception e) {
+                failure[0] = e;
+            } finally {
+                done.countDown();
+            }
+        })) {
+            throw new IllegalStateException("mirror thread stopped");
+        }
+        if (!done.await(SYNC_TIMEOUT_MS, TimeUnit.MILLISECONDS)) {
+            throw new IllegalStateException("mirror thread does not answer");
+        }
+        if (failure[0] != null) throw failure[0];
+    }
+
+    private void setUp(Surface target) {
+        display = EGL14.eglGetDisplay(EGL14.EGL_DEFAULT_DISPLAY);
+        int[] version = new int[2];
+        if (display == EGL14.EGL_NO_DISPLAY || !EGL14.eglInitialize(display, version, 0, version, 1)) {
+            throw new IllegalStateException("EGL display: " + eglError());
+        }
+        int[] attribs = {
+                EGL14.EGL_RED_SIZE, 8, EGL14.EGL_GREEN_SIZE, 8, EGL14.EGL_BLUE_SIZE, 8,
+                EGL14.EGL_RENDERABLE_TYPE, EGL14.EGL_OPENGL_ES2_BIT,
+                EGL14.EGL_SURFACE_TYPE, EGL14.EGL_WINDOW_BIT,
+                EGL14.EGL_NONE,
+        };
+        EGLConfig[] configs = new EGLConfig[1];
+        int[] count = new int[1];
+        if (!EGL14.eglChooseConfig(display, attribs, 0, configs, 0, 1, count, 0) || count[0] < 1) {
+            throw new IllegalStateException("EGL config: " + eglError());
+        }
+        context = EGL14.eglCreateContext(display, configs[0], EGL14.EGL_NO_CONTEXT,
+                new int[] {EGL14.EGL_CONTEXT_CLIENT_VERSION, 2, EGL14.EGL_NONE}, 0);
+        if (context == EGL14.EGL_NO_CONTEXT) throw new IllegalStateException("EGL context: " + eglError());
+        window = EGL14.eglCreateWindowSurface(display, configs[0], target,
+                new int[] {EGL14.EGL_NONE}, 0);
+        if (window == EGL14.EGL_NO_SURFACE) throw new IllegalStateException("EGL surface: " + eglError());
+        if (!EGL14.eglMakeCurrent(display, window, window, context)) {
+            throw new IllegalStateException("EGL current: " + eglError());
+        }
+
+        program = link(compile(GLES20.GL_VERTEX_SHADER, VERTEX),
+                compile(GLES20.GL_FRAGMENT_SHADER, FRAGMENT));
+        uMvp = GLES20.glGetUniformLocation(program, "uMvp");
+        uSt = GLES20.glGetUniformLocation(program, "uSt");
+        aPos = GLES20.glGetAttribLocation(program, "aPos");
+        aTex = GLES20.glGetAttribLocation(program, "aTex");
+
+        int[] tex = new int[1];
+        GLES20.glGenTextures(1, tex, 0);
+        texture = tex[0];
+        GLES20.glBindTexture(GLES11Ext.GL_TEXTURE_EXTERNAL_OES, texture);
+        GLES20.glTexParameteri(GLES11Ext.GL_TEXTURE_EXTERNAL_OES, GLES20.GL_TEXTURE_MIN_FILTER,
+                GLES20.GL_LINEAR);
+        GLES20.glTexParameteri(GLES11Ext.GL_TEXTURE_EXTERNAL_OES, GLES20.GL_TEXTURE_MAG_FILTER,
+                GLES20.GL_LINEAR);
+        GLES20.glTexParameteri(GLES11Ext.GL_TEXTURE_EXTERNAL_OES, GLES20.GL_TEXTURE_WRAP_S,
+                GLES20.GL_CLAMP_TO_EDGE);
+        GLES20.glTexParameteri(GLES11Ext.GL_TEXTURE_EXTERNAL_OES, GLES20.GL_TEXTURE_WRAP_T,
+                GLES20.GL_CLAMP_TO_EDGE);
+
+        surfaceTexture = new SurfaceTexture(texture);
+        surfaceTexture.setOnFrameAvailableListener(this, handler);
+        input = new Surface(surfaceTexture);
+    }
+
+    @Override
+    public void onFrameAvailable(SurfaceTexture t) {
+        // On the GL thread (the listener's handler)
+        if (released || t != surfaceTexture) return;
+        try {
+            surfaceTexture.updateTexImage();
+            surfaceTexture.getTransformMatrix(st);
+            int[] size = new int[2];
+            EGL14.eglQuerySurface(display, window, EGL14.EGL_WIDTH, size, 0);
+            EGL14.eglQuerySurface(display, window, EGL14.EGL_HEIGHT, size, 1);
+            GLES20.glViewport(0, 0, size[0], size[1]);
+            GLES20.glClearColor(0f, 0f, 0f, 1f);
+            GLES20.glClear(GLES20.GL_COLOR_BUFFER_BIT);
+            GLES20.glUseProgram(program);
+            GLES20.glActiveTexture(GLES20.GL_TEXTURE0);
+            GLES20.glBindTexture(GLES11Ext.GL_TEXTURE_EXTERNAL_OES, texture);
+            GLES20.glUniformMatrix4fv(uMvp, 1, false, mvp, 0);
+            GLES20.glUniformMatrix4fv(uSt, 1, false, st, 0);
+            quad.position(0);
+            GLES20.glVertexAttribPointer(aPos, 2, GLES20.GL_FLOAT, false, 16, quad);
+            GLES20.glEnableVertexAttribArray(aPos);
+            quad.position(2);
+            GLES20.glVertexAttribPointer(aTex, 2, GLES20.GL_FLOAT, false, 16, quad);
+            GLES20.glEnableVertexAttribArray(aTex);
+            GLES20.glDrawArrays(GLES20.GL_TRIANGLE_STRIP, 0, 4);
+            if (EGL14.eglSwapBuffers(display, window)) framesDrawn++;
+        } catch (RuntimeException e) {
+            // The surface went away meanwhile (view or activity change): the owner releases us
+            Log.w(TAG, "Mirror frame: " + e.getMessage());
+        }
+    }
+
+    private void tearDown() {
+        released = true;
+        if (surfaceTexture != null) {
+            surfaceTexture.setOnFrameAvailableListener(null);
+            surfaceTexture.release();
+            surfaceTexture = null;
+        }
+        if (input != null) {
+            input.release();
+            input = null;
+        }
+        if (display != EGL14.EGL_NO_DISPLAY) {
+            if (program != 0) GLES20.glDeleteProgram(program);
+            if (texture != 0) GLES20.glDeleteTextures(1, new int[] {texture}, 0);
+            EGL14.eglMakeCurrent(display, EGL14.EGL_NO_SURFACE, EGL14.EGL_NO_SURFACE,
+                    EGL14.EGL_NO_CONTEXT);
+            // Destroying the EGL surface frees the view's surface for a plain decoder again
+            if (window != EGL14.EGL_NO_SURFACE) EGL14.eglDestroySurface(display, window);
+            if (context != EGL14.EGL_NO_CONTEXT) EGL14.eglDestroyContext(display, context);
+            EGL14.eglReleaseThread();
+            // No eglTerminate(): the display is shared with the other mirrored cells
+        }
+        window = EGL14.EGL_NO_SURFACE;
+        context = EGL14.EGL_NO_CONTEXT;
+        display = EGL14.EGL_NO_DISPLAY;
+        program = 0;
+        texture = 0;
+    }
+
+    private static int compile(int type, String source) {
+        int shader = GLES20.glCreateShader(type);
+        GLES20.glShaderSource(shader, source);
+        GLES20.glCompileShader(shader);
+        int[] ok = new int[1];
+        GLES20.glGetShaderiv(shader, GLES20.GL_COMPILE_STATUS, ok, 0);
+        if (ok[0] == 0) {
+            String log = GLES20.glGetShaderInfoLog(shader);
+            GLES20.glDeleteShader(shader);
+            throw new IllegalStateException("shader: " + log);
+        }
+        return shader;
+    }
+
+    private static int link(int vertex, int fragment) {
+        int p = GLES20.glCreateProgram();
+        GLES20.glAttachShader(p, vertex);
+        GLES20.glAttachShader(p, fragment);
+        GLES20.glLinkProgram(p);
+        GLES20.glDeleteShader(vertex);
+        GLES20.glDeleteShader(fragment);
+        int[] ok = new int[1];
+        GLES20.glGetProgramiv(p, GLES20.GL_LINK_STATUS, ok, 0);
+        if (ok[0] == 0) {
+            String log = GLES20.glGetProgramInfoLog(p);
+            GLES20.glDeleteProgram(p);
+            throw new IllegalStateException("program: " + log);
+        }
+        return p;
+    }
+
+    private static String eglError() {
+        return "0x" + Integer.toHexString(EGL14.eglGetError());
+    }
+}
diff --git a/android/app/src/main/java/com/openipc/decoder/JpegRenderer.java b/android/app/src/main/java/com/openipc/decoder/JpegRenderer.java
index deb38f8..e9b258c 100644
--- a/android/app/src/main/java/com/openipc/decoder/JpegRenderer.java
+++ b/android/app/src/main/java/com/openipc/decoder/JpegRenderer.java
@@ -44,15 +44,17 @@ final class JpegRenderer {
 
     /**
      * Shows one frame on {@code s}, turned {@code rotate} degrees counter-clockwise (0, 90,
-     * 180 or 270, #200). Returns its {width, height} as shown (turned) when it is on screen,
+     * 180 or 270, #200), then flipped left↔right on the screen when {@code mirror} (#226). Returns its {width, height} as shown (turned) when it is on screen,
      * null when not (yet). {@code current} is false once the stream or the surface has been
      * replaced.
      */
-    int[] render(Frame frame, Surface s, int rotate, JpegCodec.Current current) {
+    int[] render(Frame frame, Surface s, int rotate, boolean mirror, JpegCodec.Current current) {
         if (s == null || !s.isValid() || !current.holds()) return null;
         // The hardware JPEG decoder first, where there is one (#132); it turns the frame itself
-        // from Android 6 on (#201), before that a turned frame is drawn by the app (#200)
-        boolean hwTurns = rotate == 0 || Build.VERSION.SDK_INT >= Build.VERSION_CODES.M;
+        // from Android 6 on (#201), before that a turned frame is drawn by the app (#200). It
+        // cannot mirror: a mirrored frame is drawn by the app (#226)
+        boolean hwTurns = !mirror
+                && (rotate == 0 || Build.VERSION.SDK_INT >= Build.VERSION_CODES.M);
         if (hwTurns && !hwFailed && !drawn && JpegCodec.candidate() != null) {
             int[] size = JpegAssembler.size(frame.data(), frame.length());
             if (size != null) {
@@ -90,6 +92,8 @@ int[] render(Frame frame, Surface s, int rotate, JpegCodec.Current current) {
             Canvas c = s.lockCanvas(null);
             try {
                 c.drawColor(Color.BLACK);
+                // Flipped on the screen, after the turn (#226)
+                if (mirror) c.scale(-1f, 1f, c.getWidth() / 2f, c.getHeight() / 2f);
                 if (rotate == 0) {
                     c.drawBitmap(b, null, new Rect(0, 0, c.getWidth(), c.getHeight()), paint);
                 } else {
diff --git a/android/app/src/main/java/com/openipc/decoder/MediaCodecManager.java b/android/app/src/main/java/com/openipc/decoder/MediaCodecManager.java
index 99b0119..2fe71bf 100644
--- a/android/app/src/main/java/com/openipc/decoder/MediaCodecManager.java
+++ b/android/app/src/main/java/com/openipc/decoder/MediaCodecManager.java
@@ -60,6 +60,12 @@ class MediaCodecManager {
     private volatile int rotation;
     /** The turn the current decoder applies: {@link #rotation} where Android 6+ can, else 0. */
     private volatile int appliedRotation;
+    /** Mirror the picture (#226): the decoder renders through {@link GlMirror}. */
+    private volatile boolean mirror;
+    /** The GL path of the current decoder (decoderLock), released after the decoder. */
+    private GlMirror glMirror;
+    /** The current decoder draws mirrored. */
+    private volatile boolean mirrored;
 
     /** Frames rendered so far (#82): with the frames received this gives the real decode rate. */
     private volatile int framesOut;
@@ -269,6 +275,25 @@ void setRotation(int degreesCcw) {
         rotation = ((degreesCcw % 360) + 360) % 360;
     }
 
+    /** See {@link #mirror}; takes effect with the next decoder. */
+    void setMirror(boolean on) {
+        mirror = on;
+    }
+
+    /** The current decoder's picture is mirrored (#226). */
+    boolean isMirrored() { return mirrored && decoder != null; }
+
+    /** Detach the GL path of the current decoder (decoderLock held), like {@link #takeSlot}. */
+    private GlMirror takeMirror() {
+        GlMirror g = glMirror;
+        glMirror = null;
+        return g;
+    }
+
+    private static void releaseMirror(GlMirror g) {
+        if (g != null) g.release();
+    }
+
     /** Enable or disable decoding; disabling also releases the decoder. */
     /**
      * Enable or disable decoding. Never blocks the caller (the UI thread): disabling only
@@ -283,13 +308,17 @@ void setEnabled(boolean enabled) {
         if (target == null) return;
         new Thread(() -> {
             String slot;
+            GlMirror gl;
             synchronized (decoderLock) {
                 if (decoder != target) return; // already replaced or released
                 decoder = null;
                 slot = takeSlot();
+                gl = takeMirror();
                 retry.onSuccess();
             }
             releaseNow(target);
+            // After the decoder: its output must be gone before GL leaves the surface
+            releaseMirror(gl);
             releaseSlot(slot);
         }, "decoder-release").start();
     }
@@ -299,8 +328,11 @@ private static void releaseNow(MediaCodec codec) {
         try { codec.release(); } catch (Exception ignored) {}
     }
 
-    private static void releaseAsync(MediaCodec codec) {
-        new Thread(() -> releaseNow(codec), "decoder-release").start();
+    private static void releaseAsync(MediaCodec codec, GlMirror gl) {
+        new Thread(() -> {
+            releaseNow(codec);
+            releaseMirror(gl);
+        }, "decoder-release").start();
     }
 
     /** Release the decoder on purpose (codec switch, camera switch): no back-off. */
@@ -322,6 +354,7 @@ private void closeDecoderLocked() {
             if (codec == null) return;
             decoder = null;
             String slot = takeSlot();
+            GlMirror gl = takeMirror();
             Log.i(TAG, "Close video decoder");
             try {
                 codec.stop();
@@ -329,6 +362,7 @@ private void closeDecoderLocked() {
             } catch (Exception e) {
                 Log.e(TAG, "Decoder close exception", e);
             }
+            releaseMirror(gl);
             releaseSlot(slot);
         }
     }
@@ -379,6 +413,7 @@ void createDecoder(boolean codecH265) {
         final String slot = software ? softwareSlot(type) : type;
 
         MediaCodec local;
+        GlMirror gl = null;
         try {
             if (software) {
                 Log.i(TAG, "Start software video decoder " + softwareName
@@ -390,19 +425,35 @@ void createDecoder(boolean codecH265) {
                 learnLimits(local, type);
             }
             int turn = rotation;
-            if (turn != 0 && Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
+            Surface target = s;
+            if (mirror) {
+                // Mirrored (#226): drawn with GL, which turns the picture as well
+                try {
+                    gl = GlMirror.create(s, turn, true);
+                    target = gl.input();
+                    Log.i(TAG, "Mirrored picture" + (turn != 0 ? ", turned " + turn
+                            + "\u00b0 counter-clockwise" : "") + " (drawn with OpenGL ES)");
+                } catch (Exception e) {
+                    Log.w(TAG, "Mirror unavailable, the picture is shown as it comes: "
+                            + e.getMessage());
+                    gl = null;
+                }
+            }
+            if (gl == null && turn != 0 && Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
                 // The decoder turns its output on the surface: clockwise degrees here (#201)
                 format.setInteger(MediaFormat.KEY_ROTATION, (360 - turn) % 360);
-            } else {
+            } else if (gl == null) {
                 turn = 0;
             }
             appliedRotation = turn;
             try {
-                local.configure(format, s, null, 0);
+                local.configure(format, target, null, 0);
                 local.start();
                 if (listener != null) listener.onDecoderStarted();
             } catch (Exception e) {
                 local.release();
+                releaseMirror(gl);
+                gl = null;
                 throw e;
             }
         } catch (Exception e) {
@@ -421,10 +472,12 @@ void createDecoder(boolean codecH265) {
             // Disabled meanwhile (pause/stop) or another thread was faster
             if (decoder != null || !enabled || gen != lifecycle) {
                 InstanceBudget.release(slot);
-                releaseAsync(local);
+                releaseAsync(local, gl);
                 return;
             }
             decoder = local;
+            glMirror = gl;
+            mirrored = gl != null;
             // A software decoder holds a slot of its own budget, not of the hardware one
             heldMime = slot;
             softwareInUse = software;
@@ -499,11 +552,13 @@ boolean decodeFrame(Frame buffer, boolean codecH265, long watchdogRef) {
                 } catch (Exception e) {
                     decoder = null;
                     String slot = takeSlot();
+                    GlMirror gl = takeMirror();
                     retry.onFailure(nowMs());
                     Log.e(TAG, "Codec exception, retry in "
                             + DecoderRetry.delayMs(retry.failures()) + " ms: " + e.getMessage());
                     try { codec.stop(); } catch (Exception ignored) {}
                     try { codec.release(); } catch (Exception ignored) {}
+                    releaseMirror(gl);
                     releaseSlot(slot);
                     if (listener != null) listener.onDecoderFailed();
                 }
diff --git a/android/app/src/main/java/com/openipc/decoder/MenuManager.java b/android/app/src/main/java/com/openipc/decoder/MenuManager.java
index 7a63b80..7687e08 100644
--- a/android/app/src/main/java/com/openipc/decoder/MenuManager.java
+++ b/android/app/src/main/java/com/openipc/decoder/MenuManager.java
@@ -27,6 +27,7 @@
 import android.webkit.HttpAuthHandler;
 import android.webkit.WebView;
 import android.webkit.WebViewClient;
+import android.widget.CheckBox;
 import android.widget.EditText;
 import android.widget.HorizontalScrollView;
 import android.widget.LinearLayout;
@@ -542,7 +543,7 @@ private EditText createEdit(String title) {
     }
 
     void showUrlEditor(int mActive, String[] mHosts, Transport.Mode[] mTransports,
-            int[] mRotates) {
+            int[] mRotates, boolean[] mMirrors) {
         AlertDialog.Builder builder = new AlertDialog.Builder(activity);
         builder.setTitle("Camera " + (mActive + 1) + " URL");
 
@@ -589,6 +590,11 @@ void showUrlEditor(int mActive, String[] mHosts, Transport.Mode[] mTransports,
         HorizontalScrollView turnRow = new HorizontalScrollView(activity);
         turnRow.addView(turn);
         content.addView(turnRow);
+        // Mirror of the picture (#226): left↔right, after the turn
+        CheckBox mirror = new CheckBox(activity);
+        mirror.setText("Mirror");
+        mirror.setChecked(mMirrors[mActive]);
+        content.addView(mirror);
         builder.setView(content);
 
         final int slot = mActive;
@@ -599,6 +605,7 @@ void showUrlEditor(int mActive, String[] mHosts, Transport.Mode[] mTransports,
             if (checked != null) mTransports[slot] = (Transport.Mode) checked.getTag();
             View turned = turn.findViewById(turn.getCheckedRadioButtonId());
             if (turned != null) mRotates[slot] = (Integer) turned.getTag();
+            mMirrors[slot] = mirror.isChecked();
             if (listener != null) listener.onSaveSettings(); // triggers save + reconnect
         });
         builder.setNegativeButton("Cancel", (dialog, which) -> dialog.cancel());
diff --git a/android/app/src/main/java/com/openipc/decoder/QuadCell.java b/android/app/src/main/java/com/openipc/decoder/QuadCell.java
index 46a9350..427d3d6 100644
--- a/android/app/src/main/java/com/openipc/decoder/QuadCell.java
+++ b/android/app/src/main/java/com/openipc/decoder/QuadCell.java
@@ -442,6 +442,9 @@ static boolean isKeyFrameNal(int type, boolean h265) {
     /** Degrees counter-clockwise the frames are turned (#200, #201), 0 for none. */
     int rotate() { return session.rotate(); }
     void setSlotTurn(int rotate) { session.setSlotTurn(rotate); }
+    /** The slot's Mirror (#226). */
+    boolean mirror() { return session.mirror(); }
+    void setSlotMirror(boolean on) { session.setSlotMirror(on); }
 
     /** Transport in use, with the mode after a fallback (#112). */
     String transportLabel() { return Transport.label(session.transportInUse(), transport); }
@@ -698,6 +701,7 @@ private void decode(Frame buffer) {
             if (s == null || !s.isValid()) return;
             decoder.setSurface(s);
             decoder.setRotation(session.rotate());
+            decoder.setMirror(session.mirror());
             decoder.createDecoder(codecH265);
             // Feed the frame that triggered creation (often the SPS) to the new decoder
             decoder.decodeFrame(buffer, codecH265, 0);
@@ -737,7 +741,7 @@ private void decodeJpeg(Frame frame) {
             return;
         }
         Surface s = surface;
-        int[] size = jpegRenderer.render(frame, s, session.rotate(),
+        int[] size = jpegRenderer.render(frame, s, session.rotate(), session.mirror(),
                 () -> running && jpeg && s == surface);
         if (size == null) return;
         lastJpegDecodeMs = now;
diff --git a/android/app/src/main/java/com/openipc/decoder/RtspClient.java b/android/app/src/main/java/com/openipc/decoder/RtspClient.java
index eabc4c6..885fb0e 100644
--- a/android/app/src/main/java/com/openipc/decoder/RtspClient.java
+++ b/android/app/src/main/java/com/openipc/decoder/RtspClient.java
@@ -98,6 +98,9 @@ void configure(String host, String userAgent, Transport.Mode transport) {
     /** Degrees counter-clockwise the MJPEG frames are turned (#200), 0 for none. */
     int rotate() { return session.rotate(); }
     void setSlotTurn(int rotate) { session.setSlotTurn(rotate); }
+    /** The slot's Mirror (#226). */
+    boolean mirror() { return session.mirror(); }
+    void setSlotMirror(boolean on) { session.setSlotMirror(on); }
 
     void start() {
         nalAssembler.reset();
diff --git a/android/app/src/main/java/com/openipc/decoder/RtspSession.java b/android/app/src/main/java/com/openipc/decoder/RtspSession.java
index fbd1789..1ae256c 100644
--- a/android/app/src/main/java/com/openipc/decoder/RtspSession.java
+++ b/android/app/src/main/java/com/openipc/decoder/RtspSession.java
@@ -710,6 +710,12 @@ int rotate() {
         return t >= 0 ? t : rotate;
     }
 
+    /** The slot's Mirror setting (#226): the picture flipped left↔right. */
+    private volatile boolean slotMirror;
+
+    boolean mirror() { return slotMirror; }
+    void setSlotMirror(boolean on) { slotMirror = on; }
+
     /** The slot's own turn (#201): -1 leaves it to the URL or the toy's default. */
     void setSlotTurn(int rotate) {
         int t = rotate == 0 || rotate == 90 || rotate == 180 || rotate == 270 ? rotate : -1;
diff --git a/android/app/src/test/java/com/openipc/decoder/GlMirrorTest.java b/android/app/src/test/java/com/openipc/decoder/GlMirrorTest.java
new file mode 100644
index 0000000..416d39e
--- /dev/null
+++ b/android/app/src/test/java/com/openipc/decoder/GlMirrorTest.java
@@ -0,0 +1,47 @@
+/*
+ * Copyright (c) OpenIPC  https://openipc.org  Prosperity Public License 3.0.0
+ *
+ * GlMirrorTest.java — where the mirrored and turned picture lands (#226)
+ *
+ */
+
+package com.openipc.decoder;
+
+import static org.junit.Assert.assertArrayEquals;
+
+import org.junit.Test;
+
+public class GlMirrorTest {
+    private static final float E = 1e-6f;
+
+    /** The picture's right edge centre (1, 0) and top edge centre (0, 1), as shown. */
+    private static void lands(int turn, boolean mirror, float[] right, float[] top) {
+        float[] m = GlMirror.transform(turn, mirror);
+        assertArrayEquals(right, GlMirror.map(m, 1f, 0f), E);
+        assertArrayEquals(top, GlMirror.map(m, 0f, 1f), E);
+    }
+
+    @Test
+    public void mirrorSwapsLeftAndRight() {
+        lands(0, false, new float[] {1f, 0f}, new float[] {0f, 1f});
+        lands(0, true, new float[] {-1f, 0f}, new float[] {0f, 1f});
+    }
+
+    @Test
+    public void turnIsCounterClockwise() {
+        // 90° ↺: the right edge goes up, the top goes left
+        lands(90, false, new float[] {0f, 1f}, new float[] {-1f, 0f});
+        lands(180, false, new float[] {-1f, 0f}, new float[] {0f, -1f});
+        lands(270, false, new float[] {0f, -1f}, new float[] {1f, 0f});
+        lands(-90, false, new float[] {0f, -1f}, new float[] {1f, 0f});
+    }
+
+    @Test
+    public void mirrorComesAfterTheTurn() {
+        // Turned first, then flipped on the screen: the top stays on the screen's top half
+        // for 0° and 180°, and goes right instead of left for 90°
+        lands(90, true, new float[] {0f, 1f}, new float[] {1f, 0f});
+        lands(180, true, new float[] {1f, 0f}, new float[] {0f, -1f});
+        lands(270, true, new float[] {0f, -1f}, new float[] {-1f, 0f});
+    }
+}
diff --git a/docs/debug.md b/docs/debug.md
index 083d0ef..d51b218 100644
--- a/docs/debug.md
+++ b/docs/debug.md
@@ -171,7 +171,7 @@ Single view and U view: every cell of the grid as the debug page shows it (3×3
 | `codec`, `size`             | when found                                          |
 | `fps`, `kbps`, `key_frames` | measured during the check                           |
 
-Toy drone slots ([toys.md](toys.md#flow-ufo)) add a `flowufo` object per cell and in `single` (`jieli` for `jieli://` slots, [toys.md](toys.md#hf--jieli-toys)), and a `heartbeat` object for RTSP slots that send the KY UFO heartbeat, and `rotate` (degrees counter-clockwise) where the picture is turned ([toys.md](toys.md#ky-ufo-rtsp-toys)).
+Toy drone slots ([toys.md](toys.md#flow-ufo)) add a `flowufo` object per cell and in `single` (`jieli` for `jieli://` slots, [toys.md](toys.md#hf--jieli-toys)), and a `heartbeat` object for RTSP slots that send the KY UFO heartbeat, and `rotate` (degrees counter-clockwise) where the picture is turned ([toys.md](toys.md#ky-ufo-rtsp-toys)), and `mirror: true` where it is mirrored ([usage.md](usage.md)).
 
 ## Log
 
diff --git a/docs/usage.md b/docs/usage.md
index 4622346..2447b96 100644
--- a/docs/usage.md
+++ b/docs/usage.md
@@ -17,7 +17,8 @@
 1. Open the menu: tap the screen, or press **OK** on a remote.
 2. Choose a slot (**1**–**8**), then **Settings**.
 3. Enter the camera URL, for example `rtsp://user:password@192.168.1.10:554/stream=0`, and choose the transport under it (**TCP / UDP / Auto / Multicast**, a new slot starts on Auto). URL formats: [transports.md](transports.md).
-   Below them, **Turn** (**Auto**, **0°**, **90° ↺**, **180°**, **270° ↺**, counter-clockwise) turns the picture of a camera mounted sideways or upside down ([#201](https://github.com/OpenIPC/decoder/issues/201)). **Auto** leaves it to the URL's `?rotate=` and the toys' defaults. It applies in the single view and in the grid, to H.264, H.265 and MJPEG, and to snapshots and screenshots; the decoder turns the picture (Android 6+; before that only MJPEG is turned). A mirror setting is not there yet: the video surface cannot be mirrored without a separate drawing path.
+   Below them, **Turn** (**Auto**, **0°**, **90° ↺**, **180°**, **270° ↺**, counter-clockwise) turns the picture of a camera mounted sideways or upside down ([#201](https://github.com/OpenIPC/decoder/issues/201)). **Auto** leaves it to the URL's `?rotate=` and the toys' defaults. It applies in the single view and in the grid, to H.264, H.265 and MJPEG, and to snapshots and screenshots; the decoder turns the picture (Android 6+; before that only MJPEG is turned).
+   **Mirror** flips the picture left to right, after the turn ([#226](https://github.com/OpenIPC/decoder/issues/226)), in the single view and in the grid, for H.264, H.265 and MJPEG, and in snapshots and screenshots. A mirrored H.264/H.265 slot is drawn with OpenGL ES instead of straight by the decoder (this path also turns it, on any Android version); a mirrored MJPEG slot is decoded in software.
 4. **Save**. The app connects at once and reconnects by itself when the stream drops (exponential back-off, 1 s up to 30 s).
 
 The URL dialog is titled `Camera N URL`. The picture is fitted to the screen whatever its shape, without cropping. URLs are stored encrypted, see [security.md](security.md#credential-store).
@@ -39,7 +40,7 @@ The menu is one grid: the eight slots on top, two rows of four below. Every word
 | Item         | Action                                                                                                                                                                                                                                                   |
 |--------------|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
 | **1**–**8**  | Switch to a camera slot (single view). The number of the active slot shows the connection quality: green under 100 ms of jitter, yellow 100–300 ms, red above. A grey number is an empty slot                                                            |
-| **Settings** | URL, transport and turn of the active slot. Single view only, grey elsewhere                                                                                                                                                                             |
+| **Settings** | URL, transport, turn and mirror of the active slot. Single view only, grey elsewhere                                                                                                                                                                     |
 | **WebUI**    | The camera's web interface, see [WebUI](#webui). Single view only, grey elsewhere                                                                                                                                                                        |
 | **Grid**     | The view: [multi-view](#multi-view) (2×2 or 3×3) or the single camera. Does not change the playback mode                                                                                                                                                 |
 | **Slides**   | The playback mode: every frame, or key frames only, see [Slides](#slides). Does not change the view                                                                                                                                                      |

From bb66c729090977f659b1f68e1eb60abc5947b811 Mon Sep 17 00:00:00 2001
From: Compot Developer <compot@openipc.org>
Date: Mon, 19 Oct 2026 21:42:10 +0000
Subject: [PATCH 2/6] fix: a decode thread from before a restart no longer
 makes the decoder (#226)

Saving the settings restarts the single view. The old decode thread was
still busy with a frame, created a decoder with the old turn and mirror,
and won the race against the new thread; the new one's attempt failed on
the busy surface and still left its turn in appliedRotation, so the
picture had the new layout but the old orientation. Now the old thread
stops before creating a decoder, closeDecoder() discards a creation that
is still running, and appliedRotation is set only by the decoder that
stays.
---
 .../app/src/main/java/com/openipc/decoder/Decoder.java    | 6 ++++++
 .../main/java/com/openipc/decoder/MediaCodecManager.java  | 8 +++++++-
 2 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/android/app/src/main/java/com/openipc/decoder/Decoder.java b/android/app/src/main/java/com/openipc/decoder/Decoder.java
index 8d11f02..251d1c2 100755
--- a/android/app/src/main/java/com/openipc/decoder/Decoder.java
+++ b/android/app/src/main/java/com/openipc/decoder/Decoder.java
@@ -2386,6 +2386,12 @@ && drawJpeg(buffer, gen)) {
                         framePool.recycle(buffer);
                     } else if (buffer != null) {
                         if (videoDecoder.decodeFrame(buffer, codecH265, 0)) {
+                            // Restarted meanwhile (new settings): the new thread makes the
+                            // decoder, with the new turn and mirror (#226)
+                            if (gen != listenerGen) {
+                                framePool.recycle(buffer);
+                                break;
+                            }
                             createDecoder();
                             // The frame that triggered creation (often the SPS) goes in too
                             videoDecoder.decodeFrame(buffer, codecH265, 0);
diff --git a/android/app/src/main/java/com/openipc/decoder/MediaCodecManager.java b/android/app/src/main/java/com/openipc/decoder/MediaCodecManager.java
index 2fe71bf..6b56578 100644
--- a/android/app/src/main/java/com/openipc/decoder/MediaCodecManager.java
+++ b/android/app/src/main/java/com/openipc/decoder/MediaCodecManager.java
@@ -347,6 +347,9 @@ void closeDecoder() {
 
     private void closeDecoderLocked() {
         synchronized (decoderLock) {
+            // A creation still running (another thread, older settings) is discarded when it
+            // ends: it must not replace the decoder the caller will make next (#226)
+            lifecycle++;
             retry.onSuccess();
             MediaCodec codec = decoder;
             // The next stream must not look live because of this one's last frame
@@ -414,6 +417,7 @@ void createDecoder(boolean codecH265) {
 
         MediaCodec local;
         GlMirror gl = null;
+        int turnApplied = 0;
         try {
             if (software) {
                 Log.i(TAG, "Start software video decoder " + softwareName
@@ -445,7 +449,7 @@ void createDecoder(boolean codecH265) {
             } else if (gl == null) {
                 turn = 0;
             }
-            appliedRotation = turn;
+            turnApplied = turn;
             try {
                 local.configure(format, target, null, 0);
                 local.start();
@@ -478,6 +482,8 @@ void createDecoder(boolean codecH265) {
             decoder = local;
             glMirror = gl;
             mirrored = gl != null;
+            // Only the decoder that stays sets these: a creation that lost must not (#226)
+            appliedRotation = turnApplied;
             // A software decoder holds a slot of its own budget, not of the hardware one
             heldMime = slot;
             softwareInUse = software;

From 30402e8e7dd66a424c7a79351e159d09aaf4aa37 Mon Sep 17 00:00:00 2001
From: Compot Developer <compot@openipc.org>
Date: Mon, 19 Oct 2026 21:29:25 +0000
Subject: [PATCH 3/6] chore: version 2.18.0

---
 CHANGELOG.md             | 6 ++++++
 android/app/build.gradle | 4 ++--
 2 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 2375ab3..1ecd0cd 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -12,6 +12,12 @@ Versions after 2.17 are `MAJOR.MINOR.PATCH` (2.17 is followed by 2.17.1 or 2.18.
 `docs/testing.md`, "Versions and releases"); the headings below keep the numbers as they
 were released.
 
+## 2.18.0 — 2026-10-19
+
+- Mirror in the camera settings, next to Turn: flips the picture left to right in the single
+  view and the grid, for H.264, H.265 and MJPEG; a mirrored H.264/H.265 slot is drawn with
+  OpenGL ES (PR #246, closes #226).
+
 ## 2.17 — 2026-10-17
 
 - Turn in the camera settings (Auto, 0°, 90°, 180°, 270°), stored per slot; H.264/H.265 are
diff --git a/android/app/build.gradle b/android/app/build.gradle
index f6bbe65..ab89f64 100755
--- a/android/app/build.gradle
+++ b/android/app/build.gradle
@@ -23,8 +23,8 @@ android {
         applicationId "com.openipc.decoder"
         minSdk 21
         targetSdk 36
-        versionCode 42
-        versionName "2.17"
+        versionCode 43
+        versionName "2.18.0"
 
         buildConfigField "String", "GIT_HASH", "\"${getGitHash()}\""
     }

From 3880236e8a0420a27807176f8b25a8ede86a6306 Mon Sep 17 00:00:00 2001
From: Compot Developer <compot@openipc.org>
Date: Tue, 20 Oct 2026 08:15:33 +0000
Subject: [PATCH 4/6] =?UTF-8?q?fix:=20Mirror=20review=20fixes=20=E2=80=94?=
 =?UTF-8?q?=20restart=20race,=20GL=20cleanup,=20mirror=5Ffailed=20in=20sta?=
 =?UTF-8?q?ts=20(#226)?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

- A decoder made by a video thread whose stream was restarted with new
  settings is dropped when installed, not only before creation.
- The GL path is released even when releasing a failed codec throws.
- A queued frame is no longer drawn once the GL path is being released.
- /stats.json: mirror_failed: true when Mirror is on but the GL path
  failed and the decoder draws unmirrored; unused framesDrawn removed.
---
 .../java/com/openipc/decoder/Decoder.java     | 18 +++++++++----
 .../java/com/openipc/decoder/GlMirror.java    | 10 +++-----
 .../openipc/decoder/MediaCodecManager.java    | 25 ++++++++++++++-----
 .../java/com/openipc/decoder/QuadCell.java    |  2 ++
 docs/debug.md                                 |  2 +-
 5 files changed, 39 insertions(+), 18 deletions(-)

diff --git a/android/app/src/main/java/com/openipc/decoder/Decoder.java b/android/app/src/main/java/com/openipc/decoder/Decoder.java
index 251d1c2..07a1a91 100755
--- a/android/app/src/main/java/com/openipc/decoder/Decoder.java
+++ b/android/app/src/main/java/com/openipc/decoder/Decoder.java
@@ -608,12 +608,14 @@ private void configureClient() {
         rtspClient.setSlotMirror(mMirrors[mActive]);
     }
 
-    private void createDecoder() {
+    /** A decoder for the stream of video thread {@code gen}, with that stream's turn and mirror. */
+    private void createDecoder(int gen) {
         videoDecoder.setSurface(mVideoSurface);
         RtspClient c = rtspClient;
         videoDecoder.setRotation(c != null ? c.rotate() : 0);
         videoDecoder.setMirror(c != null && c.mirror());
-        videoDecoder.createDecoder(codecH265);
+        // Restarted with new settings meanwhile: this decoder is dropped, the new thread makes one
+        videoDecoder.createDecoder(codecH265, () -> gen == listenerGen);
     }
 
     private void closeDecoder() { videoDecoder.closeDecoder(); }
@@ -1633,7 +1635,10 @@ private Map<String, Object> debugState() {
             // Turned counter-clockwise, "size" is the turned one (#200, #201)
             int rotate = rtspClient != null ? rtspClient.rotate() : 0;
             if (rotate != 0) single.put("rotate", rotate);
-            if (rtspClient != null && rtspClient.mirror()) single.put("mirror", true);
+            if (rtspClient != null && rtspClient.mirror()) {
+                single.put("mirror", true);
+                if (videoDecoder.mirrorFailed()) single.put("mirror_failed", true);
+            }
             m.put("single", single);
         }
         QuadCell[] cells = quadCells;
@@ -1679,7 +1684,10 @@ private Map<String, Object> debugState() {
                     Map<String, Object> hb = cell.heartbeatStats();
                     if (hb != null) c.put("heartbeat", hb);
                     if (cell.rotate() != 0) c.put("rotate", cell.rotate());
-                    if (cell.mirror()) c.put("mirror", true);
+                    if (cell.mirror()) {
+                        c.put("mirror", true);
+                        if (cell.mirrorFailed()) c.put("mirror_failed", true);
+                    }
                 }
                 list.add(c);
             }
@@ -2392,7 +2400,7 @@ && drawJpeg(buffer, gen)) {
                                 framePool.recycle(buffer);
                                 break;
                             }
-                            createDecoder();
+                            createDecoder(gen);
                             // The frame that triggered creation (often the SPS) goes in too
                             videoDecoder.decodeFrame(buffer, codecH265, 0);
                         }
diff --git a/android/app/src/main/java/com/openipc/decoder/GlMirror.java b/android/app/src/main/java/com/openipc/decoder/GlMirror.java
index e76c0c2..e62d861 100644
--- a/android/app/src/main/java/com/openipc/decoder/GlMirror.java
+++ b/android/app/src/main/java/com/openipc/decoder/GlMirror.java
@@ -80,8 +80,7 @@ final class GlMirror implements SurfaceTexture.OnFrameAvailableListener {
     private int uMvp, uSt, aPos, aTex;
     private SurfaceTexture surfaceTexture;
     private Surface input;
-    private boolean released;
-    private volatile int framesDrawn;
+    private volatile boolean released;
 
     private GlMirror(int turnCcw, boolean mirror) {
         mvp = transform(turnCcw, mirror);
@@ -132,11 +131,10 @@ static GlMirror create(Surface target, int turnCcw, boolean mirror) throws Excep
     /** The surface the decoder renders into. */
     Surface input() { return input; }
 
-    /** Frames drawn onto the view's surface so far. */
-    int framesDrawn() { return framesDrawn; }
-
     /** Release GL and the thread; waits until the view's surface is free again. */
     void release() {
+        // A frame already queued on the GL thread is no longer drawn (Qodo on #246)
+        released = true;
         try {
             runSync(this::tearDown);
         } catch (Exception e) {
@@ -246,7 +244,7 @@ public void onFrameAvailable(SurfaceTexture t) {
             GLES20.glVertexAttribPointer(aTex, 2, GLES20.GL_FLOAT, false, 16, quad);
             GLES20.glEnableVertexAttribArray(aTex);
             GLES20.glDrawArrays(GLES20.GL_TRIANGLE_STRIP, 0, 4);
-            if (EGL14.eglSwapBuffers(display, window)) framesDrawn++;
+            EGL14.eglSwapBuffers(display, window);
         } catch (RuntimeException e) {
             // The surface went away meanwhile (view or activity change): the owner releases us
             Log.w(TAG, "Mirror frame: " + e.getMessage());
diff --git a/android/app/src/main/java/com/openipc/decoder/MediaCodecManager.java b/android/app/src/main/java/com/openipc/decoder/MediaCodecManager.java
index 6b56578..3849537 100644
--- a/android/app/src/main/java/com/openipc/decoder/MediaCodecManager.java
+++ b/android/app/src/main/java/com/openipc/decoder/MediaCodecManager.java
@@ -280,8 +280,8 @@ void setMirror(boolean on) {
         mirror = on;
     }
 
-    /** The current decoder's picture is mirrored (#226). */
-    boolean isMirrored() { return mirrored && decoder != null; }
+    /** Mirror is on, but the current decoder draws unmirrored: the GL path failed (#226). */
+    boolean mirrorFailed() { return mirror && !mirrored && decoder != null; }
 
     /** Detach the GL path of the current decoder (decoderLock held), like {@link #takeSlot}. */
     private GlMirror takeMirror() {
@@ -375,6 +375,15 @@ private static long nowMs() {
     }
 
     void createDecoder(boolean codecH265) {
+        createDecoder(codecH265, null);
+    }
+
+    /**
+     * Like {@link #createDecoder(boolean)}; {@code current} (may be null) is checked under the
+     * lock when the decoder is installed: false once the caller's stream was restarted with
+     * other settings, and the decoder made with the old ones is dropped (Qodo on #246).
+     */
+    void createDecoder(boolean codecH265, JpegCodec.Current current) {
         final int gen;
         synchronized (decoderLock) {
             if (decoder != null || !enabled || !retry.mayCreate(nowMs())) return;
@@ -455,9 +464,12 @@ void createDecoder(boolean codecH265) {
                 local.start();
                 if (listener != null) listener.onDecoderStarted();
             } catch (Exception e) {
-                local.release();
-                releaseMirror(gl);
-                gl = null;
+                try {
+                    local.release();
+                } finally {
+                    releaseMirror(gl);
+                    gl = null;
+                }
                 throw e;
             }
         } catch (Exception e) {
@@ -474,7 +486,8 @@ void createDecoder(boolean codecH265) {
 
         synchronized (decoderLock) {
             // Disabled meanwhile (pause/stop) or another thread was faster
-            if (decoder != null || !enabled || gen != lifecycle) {
+            if (decoder != null || !enabled || gen != lifecycle
+                    || (current != null && !current.holds())) {
                 InstanceBudget.release(slot);
                 releaseAsync(local, gl);
                 return;
diff --git a/android/app/src/main/java/com/openipc/decoder/QuadCell.java b/android/app/src/main/java/com/openipc/decoder/QuadCell.java
index 427d3d6..2135ad6 100644
--- a/android/app/src/main/java/com/openipc/decoder/QuadCell.java
+++ b/android/app/src/main/java/com/openipc/decoder/QuadCell.java
@@ -444,6 +444,8 @@ static boolean isKeyFrameNal(int type, boolean h265) {
     void setSlotTurn(int rotate) { session.setSlotTurn(rotate); }
     /** The slot's Mirror (#226). */
     boolean mirror() { return session.mirror(); }
+    /** Mirror is on, but the video decoder draws unmirrored (the GL path failed). */
+    boolean mirrorFailed() { return !jpeg && decoder.mirrorFailed(); }
     void setSlotMirror(boolean on) { session.setSlotMirror(on); }
 
     /** Transport in use, with the mode after a fallback (#112). */
diff --git a/docs/debug.md b/docs/debug.md
index d51b218..a875335 100644
--- a/docs/debug.md
+++ b/docs/debug.md
@@ -171,7 +171,7 @@ Single view and U view: every cell of the grid as the debug page shows it (3×3
 | `codec`, `size`             | when found                                          |
 | `fps`, `kbps`, `key_frames` | measured during the check                           |
 
-Toy drone slots ([toys.md](toys.md#flow-ufo)) add a `flowufo` object per cell and in `single` (`jieli` for `jieli://` slots, [toys.md](toys.md#hf--jieli-toys)), and a `heartbeat` object for RTSP slots that send the KY UFO heartbeat, and `rotate` (degrees counter-clockwise) where the picture is turned ([toys.md](toys.md#ky-ufo-rtsp-toys)), and `mirror: true` where it is mirrored ([usage.md](usage.md)).
+Toy drone slots ([toys.md](toys.md#flow-ufo)) add a `flowufo` object per cell and in `single` (`jieli` for `jieli://` slots, [toys.md](toys.md#hf--jieli-toys)), and a `heartbeat` object for RTSP slots that send the KY UFO heartbeat, and `rotate` (degrees counter-clockwise) where the picture is turned ([toys.md](toys.md#ky-ufo-rtsp-toys)), and `mirror: true` where it is mirrored ([usage.md](usage.md)), with `mirror_failed: true` if the device could not mirror the video and shows it unmirrored.
 
 ## Log
 

From 4d046c365bc22fb3ab09dac35af6ff890c9d92f2 Mon Sep 17 00:00:00 2001
From: Compot Developer <compot@openipc.org>
Date: Tue, 20 Oct 2026 08:17:01 +0000
Subject: [PATCH 5/6] fix: balance eglInitialize with eglTerminate in the
 mirror's GL path (#226)

Android counts eglInitialize per display, so eglTerminate only drops this
instance's reference; other mirrored cells keep the display.
---
 .../app/src/main/java/com/openipc/decoder/GlMirror.java   | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/android/app/src/main/java/com/openipc/decoder/GlMirror.java b/android/app/src/main/java/com/openipc/decoder/GlMirror.java
index e62d861..2b88f08 100644
--- a/android/app/src/main/java/com/openipc/decoder/GlMirror.java
+++ b/android/app/src/main/java/com/openipc/decoder/GlMirror.java
@@ -81,6 +81,8 @@ final class GlMirror implements SurfaceTexture.OnFrameAvailableListener {
     private SurfaceTexture surfaceTexture;
     private Surface input;
     private volatile boolean released;
+    /** eglInitialize() succeeded: tearDown() balances it with eglTerminate(). */
+    private boolean initialized;
 
     private GlMirror(int turnCcw, boolean mirror) {
         mvp = transform(turnCcw, mirror);
@@ -173,6 +175,7 @@ private void setUp(Surface target) {
         if (display == EGL14.EGL_NO_DISPLAY || !EGL14.eglInitialize(display, version, 0, version, 1)) {
             throw new IllegalStateException("EGL display: " + eglError());
         }
+        initialized = true;
         int[] attribs = {
                 EGL14.EGL_RED_SIZE, 8, EGL14.EGL_GREEN_SIZE, 8, EGL14.EGL_BLUE_SIZE, 8,
                 EGL14.EGL_RENDERABLE_TYPE, EGL14.EGL_OPENGL_ES2_BIT,
@@ -270,9 +273,12 @@ private void tearDown() {
             // Destroying the EGL surface frees the view's surface for a plain decoder again
             if (window != EGL14.EGL_NO_SURFACE) EGL14.eglDestroySurface(display, window);
             if (context != EGL14.EGL_NO_CONTEXT) EGL14.eglDestroyContext(display, context);
+            // Android counts eglInitialize() per display: this only drops our reference, the
+            // other mirrored cells and the system renderer keep theirs (Qodo on #246)
+            if (initialized) EGL14.eglTerminate(display);
             EGL14.eglReleaseThread();
-            // No eglTerminate(): the display is shared with the other mirrored cells
         }
+        initialized = false;
         window = EGL14.EGL_NO_SURFACE;
         context = EGL14.EGL_NO_CONTEXT;
         display = EGL14.EGL_NO_DISPLAY;

From aed8dcba77e58e11422f356bf4d54061655b22d7 Mon Sep 17 00:00:00 2001
From: Compot Developer <compot@openipc.org>
Date: Tue, 20 Oct 2026 08:52:39 +0000
Subject: [PATCH 6/6] fix: a mirrored frame that cannot be drawn is logged and
 shown as mirror_failed (#226)

eglQuerySurface and eglSwapBuffers results are checked; the first failure
after setup is logged with the EGL error, and /stats.json reports
mirror_failed for that decoder.
---
 .../java/com/openipc/decoder/GlMirror.java    | 22 +++++++++++++++----
 .../openipc/decoder/MediaCodecManager.java    |  7 ++++--
 docs/debug.md                                 |  2 +-
 3 files changed, 24 insertions(+), 7 deletions(-)

diff --git a/android/app/src/main/java/com/openipc/decoder/GlMirror.java b/android/app/src/main/java/com/openipc/decoder/GlMirror.java
index 2b88f08..a3848df 100644
--- a/android/app/src/main/java/com/openipc/decoder/GlMirror.java
+++ b/android/app/src/main/java/com/openipc/decoder/GlMirror.java
@@ -81,6 +81,8 @@ final class GlMirror implements SurfaceTexture.OnFrameAvailableListener {
     private SurfaceTexture surfaceTexture;
     private Surface input;
     private volatile boolean released;
+    /** A frame could not be shown (EGL error after setup): logged once, reported in stats. */
+    private volatile boolean drawFailed;
     /** eglInitialize() succeeded: tearDown() balances it with eglTerminate(). */
     private boolean initialized;
 
@@ -130,6 +132,15 @@ static GlMirror create(Surface target, int turnCcw, boolean mirror) throws Excep
         return g;
     }
 
+    /** A frame could not be drawn since setup (Qodo on #246). */
+    boolean drawFailed() { return drawFailed; }
+
+    private void drawFailed(String why) {
+        if (released) return;
+        if (!drawFailed) Log.w(TAG, "Mirror frame not shown: " + why);
+        drawFailed = true;
+    }
+
     /** The surface the decoder renders into. */
     Surface input() { return input; }
 
@@ -230,8 +241,11 @@ public void onFrameAvailable(SurfaceTexture t) {
             surfaceTexture.updateTexImage();
             surfaceTexture.getTransformMatrix(st);
             int[] size = new int[2];
-            EGL14.eglQuerySurface(display, window, EGL14.EGL_WIDTH, size, 0);
-            EGL14.eglQuerySurface(display, window, EGL14.EGL_HEIGHT, size, 1);
+            if (!EGL14.eglQuerySurface(display, window, EGL14.EGL_WIDTH, size, 0)
+                    || !EGL14.eglQuerySurface(display, window, EGL14.EGL_HEIGHT, size, 1)) {
+                drawFailed("surface: " + eglError());
+                return;
+            }
             GLES20.glViewport(0, 0, size[0], size[1]);
             GLES20.glClearColor(0f, 0f, 0f, 1f);
             GLES20.glClear(GLES20.GL_COLOR_BUFFER_BIT);
@@ -247,10 +261,10 @@ public void onFrameAvailable(SurfaceTexture t) {
             GLES20.glVertexAttribPointer(aTex, 2, GLES20.GL_FLOAT, false, 16, quad);
             GLES20.glEnableVertexAttribArray(aTex);
             GLES20.glDrawArrays(GLES20.GL_TRIANGLE_STRIP, 0, 4);
-            EGL14.eglSwapBuffers(display, window);
+            if (!EGL14.eglSwapBuffers(display, window)) drawFailed("swap: " + eglError());
         } catch (RuntimeException e) {
             // The surface went away meanwhile (view or activity change): the owner releases us
-            Log.w(TAG, "Mirror frame: " + e.getMessage());
+            drawFailed(e.getMessage());
         }
     }
 
diff --git a/android/app/src/main/java/com/openipc/decoder/MediaCodecManager.java b/android/app/src/main/java/com/openipc/decoder/MediaCodecManager.java
index 3849537..f66ce7d 100644
--- a/android/app/src/main/java/com/openipc/decoder/MediaCodecManager.java
+++ b/android/app/src/main/java/com/openipc/decoder/MediaCodecManager.java
@@ -63,7 +63,7 @@ class MediaCodecManager {
     /** Mirror the picture (#226): the decoder renders through {@link GlMirror}. */
     private volatile boolean mirror;
     /** The GL path of the current decoder (decoderLock), released after the decoder. */
-    private GlMirror glMirror;
+    private volatile GlMirror glMirror;
     /** The current decoder draws mirrored. */
     private volatile boolean mirrored;
 
@@ -281,7 +281,10 @@ void setMirror(boolean on) {
     }
 
     /** Mirror is on, but the current decoder draws unmirrored: the GL path failed (#226). */
-    boolean mirrorFailed() { return mirror && !mirrored && decoder != null; }
+    boolean mirrorFailed() {
+        GlMirror g = glMirror;
+        return mirror && decoder != null && (!mirrored || (g != null && g.drawFailed()));
+    }
 
     /** Detach the GL path of the current decoder (decoderLock held), like {@link #takeSlot}. */
     private GlMirror takeMirror() {
diff --git a/docs/debug.md b/docs/debug.md
index a875335..0a6df3e 100644
--- a/docs/debug.md
+++ b/docs/debug.md
@@ -171,7 +171,7 @@ Single view and U view: every cell of the grid as the debug page shows it (3×3
 | `codec`, `size`             | when found                                          |
 | `fps`, `kbps`, `key_frames` | measured during the check                           |
 
-Toy drone slots ([toys.md](toys.md#flow-ufo)) add a `flowufo` object per cell and in `single` (`jieli` for `jieli://` slots, [toys.md](toys.md#hf--jieli-toys)), and a `heartbeat` object for RTSP slots that send the KY UFO heartbeat, and `rotate` (degrees counter-clockwise) where the picture is turned ([toys.md](toys.md#ky-ufo-rtsp-toys)), and `mirror: true` where it is mirrored ([usage.md](usage.md)), with `mirror_failed: true` if the device could not mirror the video and shows it unmirrored.
+Toy drone slots ([toys.md](toys.md#flow-ufo)) add a `flowufo` object per cell and in `single` (`jieli` for `jieli://` slots, [toys.md](toys.md#hf--jieli-toys)), and a `heartbeat` object for RTSP slots that send the KY UFO heartbeat, and `rotate` (degrees counter-clockwise) where the picture is turned ([toys.md](toys.md#ky-ufo-rtsp-toys)), and `mirror: true` where it is mirrored ([usage.md](usage.md)), with `mirror_failed: true` if the device could not mirror the video (it is shown unmirrored) or a mirrored frame could not be drawn.
 
 ## Log